Best guess, Simon forgot to update the website with the Linux version.
tbh, I'm surprised to see the 0.57 Windows version there - Simon was getting really bad at updating the downloads area of his own site for a while.

If you have access, you might want to try see if Steam has the 0.57 build of Maia. I know it's separately managed. I wish I could tell you, but I don't run Linux.

If I'm understanding it correctly, it basically says Steam's Linux version of Maia was updated 14 days ago. Which seems about right, since 0.57 was pushed out on the 12th of July and today is the 26th.
It also says that the Windows version was updated 8 days ago, which I'm guessing is a hotfix that hasn't been rolled out in the Linux version yet.

Either way, it looks like the Linux version is alive and well... just not in the members download area yet.